Contour control- anyone ever use it?

[imaradiostar]

I saw this on a forum somewhere ages ago and I've been meaning to use it in an ultra-simple design driven by a mosfet or cathode follower for low impedance drive.



Looks like it would cover most of the distortion EQ flavors I'd need. I'm picturing a small channel switching amp with a volume and tone for the clean channel, drive, contour and volume for the dirty and a master presence or tone cut control.

thoughts?

jamie

[guitarmike2107]

Some of the old valvestate amps had a contour control, at the time I didn’t like it. But then I don’t think back then I understood what it was doing.

I have just built an amp that uses two controls for the contour giving greater flexibility, it modifies the low mid and hi mid roll off independently, It is really fun to play and can get most clean tones from blackface fender to tweed to Marshally …

[imaradiostar]

Thanks for the practical experience.

I seem to recall most valvestate amps using the contour control in series with the normal Marshall TMB tone stack- I could see the end result being excessive.

I've been thinking with the Dr. Z school of thought recently- less is more. I'm thinking this contour control wouldn't suit clean sounds as well as distorted ones.

As usual- need to build it and see how it sounds!

jamie

[J M Fahey]

It's a very popular distortion tone control.
Maybe capable of over the top adjustment, but that's why it has a pot !!!
Build it, you'll like it.
Not that useful on clean sounds, though.

[jrfrond]

I think it has some applications. I actually like them more on bass amps than guitar amps.

The tone control on the Big Muff Pi is basically a contour control, and could be easily-adapted to amp use. I would definitely use low-impedance drive for this circuit.

A more accurate and versatile control could be built using a State-Variable filter design.

[imaradiostar]

There are a lot of useful tone controls but no others that I know of can do treble rolloff, flat, subtle treble boost, and subtle through major mid scoop on one knob. It seems like the ideal distortion tone control for that reason.

Hopefully I'll have a chance to try it this weekend.

jamie

[Gaz]

Sorry, I can't enlarge the pic (any on this forum for that matter - my computer is too old). Is it the same as the Big Muff Pi control, or something different?

Speaking of Dr. Z, he uses a mid-scoop ala Gibson as a tone control in one amp. Most folks don't even realize what it's doing because it's just labeled as "tone," but love it. Another nice alternative to the typical one-knob-treble-cut.

[imaradiostar]

Is it the same as the Big Muff Pi control, or something different?

It's pretty different from the Gibson/Dr Z control and the big muff control. It requires a low impedance source like a cathode follower or it just doesn't work correctly. Here's a link to the picture itself if you can click it:

http://music-electronics-forum.com/a...18-contour.png

I went out in the shop tonight and finished up some work on a stereo champ I built over a year ago and never finished. I didn't have time to try this control.

I have too many unfinished projects!

JT

[Steve Conner]

Looks like a nice wee circuit

I'd try it in my current build, which has a one-knob treble cut that doesn't really do much for me. But it's already quite scooped sounding, because the Eminence Beta speaker doesn't have the midrange boost of a proper guitar speaker. The last thing it needs is a midrange notch.

I have the schematic saved to try on my next one...

[TDS]

Looks just I could use for a small practice amp I thinking of building. Do I understand correctly that there is a single 100k pot? i.e. R=Pot and R=Pot2 are the same component.

[imaradiostar]

Yes, the pot is just one component.

I have a teeny tiny chassis with a pentode, 2 12ax7's and 2 6aq5's. I'm thinking it'll get this tone control and be a teeny tiny channel switcher. I'll probably buffer the effect send and distortion tone control with source followers to save triodes.

jamie

[tmod]

I think one fo the reasons is that it has huge insertion losses. According to my sim, it has an impedance of about 20k at 1kHz, even at max mid; a huge load unless driven by a CF. A Fender stack has an impedance of 100k, which is still a pretty tough load for a tube. A Marshall stack has an impedance of about 45k at 1kHz, which is double the contour control, even though 1kHz is in the middle of the scooped part of the stack setting.

I like the versatility of you stack, but it would take either a CF or an extra gain stage to get the signal back up to needed levels in a tube amp.

[Steve Conner]

Insertion loss isn't the same as input impedance.

You can change input impedance to whatever you want by scaling all the impedances of the circuit: doubling all the resistors and inductors, halving the capacitances, will keep the same frequency reponse but double the input impedance. But the insertion loss will still be the same.

For use in a tube amp I would scale this circuit by a factor of 10.

[imaradiostar]

I did some simulation a while back- this circuit works fine driven from a 47k load if it's scaled 10x. I just like the lower impedance and the ability to use parts I had laying around.

The other thing to remember- insertion loss is much less of an issue if it's the tone control for a distortion channel. The output of a marshall cathode follower can be well over a hundred volts!

jt

[Steve Conner]

Yeah, you actually need to lose as much signal as you can at that point.

But, the impedance of the source affects the frequency response of the circuit, so you probably still need that CF.